And the subordinate pigs’s habit of reclining idly by the trough is rewarded too

From Richard Dawkins book, The Selfish Gene.

The most satisfying example of a paradoxical strategy known to me involves domestic pigs in a Skinner box. The strategy is stable in the same sense an Evolutionarily Stable Strategy, but it is better called a DSS (“developmentally stable strategy”) because it arises during the animals own lifetimes rather than over evolutionary time. A Skinner box is an apparatus in which an animal learns to feed itself by pressing a lever, food then being automatically delivered down a chute. Experimental psychologists are accustomed to putting pigeons or rats in small Skinner boxes, where they soon learn to press delicate little levers for a food reward. Pigs can learn the same thing in a scaled-up Skinner box with a very undelicate snout-lever (I saw a research film of this many years ago and I recall almost dying of laughter). B. A. Baldwin and G. B. Meese trained pigs in a Skinner sty, but there is an added twist to the tale. The snout-lever was at one end of the sty; the food dispenser at the other. So the pig had to press the lever, then race up to the other end of the sty to get the food, then rush back to the lever, and so on. This sounds all very well, but Baldiwn and Meese put pairs of pigs into the apparatus. It now became possible for one pig to exploit the other. The “servant” pig rushed back and forth pressing the bar. The “master” pig sat by the food chute and ate the food as it was dispensed. Pairs of pigs did indeed settle down into a stable “master/servant” pattern of this kind, one working and running, the other doing most of the eating.

Now for the paradox. The labels “master” and “servant” turned out to be all topsy-turvy. Whenever a pair of pigs settled down to a stable pattern, the pig that ended up playing the “master” or “exploiting” role was the pig that, in all other ways, was subordinate. The so-called “servant” pig, the one that did all the work, was the pig that was usually dominant. Anybody knowing the pigs would have predicted that, on the contrary, the dominant pig would have been the master, doing most of the eating; the subordinate pig should have been the hard-working and scarcely eating servant.

How could this paradoxical reversal arise? It is easy to understand, once you start thinking in terms of stable strategies. All that we have to do is scale the idea down from evolutionary time to developmental time, the time-scale on which a relationship between two individuals develops. The strategy “If dominant, sit by the food trough; if subordinate, work the lever” sounds sensible, but would not be stable. The subordinate pig, having pressed the lever, would come sprinting over, only to find the dominant pig with its front feet firmly in the trough and impossible to dislodge. The subordinate pig would soon stop pressing the lever, for the habit would never be rewarded. But now consider the reverse strategy: “If dominant, work the lever; if subordinate, sit by the food trough.” This would be stable, even though it has the paradoxical result that the subordinate pigs gets most of the food. All that is necessary is that there should be some food left for the dominant pig when he charges up from the other end of the sty. As soon as he arrives, he has no difficulty in tossing the subordinate pig out of the trough. As long as there is a crumb left to reward him, his habit of working the lever, and thereby inadvertently stuffing the subordinate pig, will persist. And the subordinate pigs’s habit of reclining idly by the trough is rewarded too.